1. Field of the Invention
The invention relates to a diagnostic apparatus and a diagnostic method for a fuel cell and, more particularly, to a diagnostic apparatus and a diagnostic method for diagnosing a state of a fuel cell.
2. Description of the Related Art
Heretofore, there has been proposed a fuel cell system of this type which makes a determination on an abnormal operational state such as excessiveness or scarceness of water contained in a fuel cell stack (e.g., Japanese Patent Application Laid-Open No. 9-245826 (FIG. 1, FIG. 2)). In this system, time-dependent change patterns of a voltage in a cell or a cell block constituting the fuel cell stack are measured and stored in advance as to various operational conditions, and a determination on an operational state of the fuel cell stack is made by comparing an actual time-dependent pattern with the stored patterns.
In such a fuel cell system, an abnormality of the fuel cell stack is not limited to excessiveness or scarceness of water contained in a fuel cell stack, and a phenomenon caused by such an abnormality is not limited to abnormal voltage behavior in the cell or the cell block in the fuel cell stack. Therefore, since the operational state is determined based on the voltage behavior, an erroneous determination may be made. Particularly, when other abnormalities of the fuel cell stack are to be determined in addition to the aforementioned abnormalities, an appropriate determination cannot be made.